The present invention concerns a directional antenna system for deployment in outer space having means for suppressing sidelobe interference.
Several papers have been presented in the past few years which disclose the design of a new class of directional antenna having a flexible metallic membrane reflector element. The flexible membrane is shaped by electrostatic forces applied to the back side of the membrane. One such paper concerning a very large, low mass, high precision, space deployable, reflecting antenna is entitled, "Electrostatically Figured Reflecting Membrane Antennas For Satellites", and appears on pp. 666-670 of the IEEE Transactions on Automatic Control, Vol. AC-27, No. 3, June 1982. The aforementioned antenna system however, like other directional antenna systems, has undesired sidelobe responses which permit signals received from radiant sources angularly displaced from the main axis of the reflector to interfere with and sometimes jam or mask the desired signals.
Various techniques have been used in the past to reduce sidelobe interference. Generally, sidelobe suppression in directional antennas is accomplished by combining the signal from the main antenna with that of an auxilliary antenna, suitably adjusted in amplitude and phase. Such systems, however, are generally expensive to fabricate requiring high precision components and complex electronic circuitry for adequate system bandwidth.
Another technique used to reject sidelobe interference is adaptive nulling. Using this technique, a null can be placed in a sidelobe to reduce the amount of energy received from the jamming source. Adaptive nulling, however, also requires costly components, as well as complicated algorithms and long processing times.